Diagonal sweep shutter mechanism for video tape camera

ABSTRACT

A focal plane shutter for a video camera has a pair of disks rotated in the same direction about a common axis in synchronism with the raster scan blanking interval. The disks have openings which overlie one another and define a light admitting shutter aperture positioned to illuminate the video pickup. Each opening is bounded on first and second sides by lines emanating from a point on the disk which is offset from the disk&#39;s axis of rotation preferably by a distance equal to the length of the diagonal of the raster. This enables an even exposure of the video pickup, of equal areas at equal times, no matter where the pickup is positioned relative to the disk&#39;s axis of rotation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to video cameras, and moreparticularly to shutter mechanisms for video cameras. More specifically,the invention relates to improved focal plane shutters for producingstop action or slow motion pictures without blurring, skewing, ordistortion.

2. Description of the Prior Art

The capturing of physical images through video recording involves aprocess whereby light reflecting or emanating from object within a sceneis collected and converted into electrical energy, and then magneticallystored for replay at a later time. The typical video system includes anoptical system comprising one or more high quality, color-correctedlenses for focusing an image on the photosensitive surface of a videopickup device. Optical focusing is achieved by moving the lense withrespect to the pickup device or by moving the pickup device with respectto the lense. The light which reaches the photosensitive surface of thepickup tube or other pickup device represents the image of the scenebeing recorded.

The exposure or quantity of light reaching the pickup tube surface maybe controlled by varying the exposure time, by varying the size of thelense aperture or opening through which the exposure is made, or byvarying both exposure time and lense aperture size--all of which arerelated to one another through the principle of reciprocity. Theprinciple of reciprocity states generally that exposure time and lenseaperture size are inversely related and that an exposure of a givenquantity of light can be achieved by a wide variety of exposuretime/aperture size combinations. To vary the exposure time, rotary focalplane shutters are sometimes placed between the lense and the pickuptube or device. Prior art rotary focal plane shutters are discussed morefully below. To vary the lense aperture size, it is common to providethe optical system or lense with an iris diaphragm mechanism whichcomprises thin overlapping metal plates that can be adjusted to form anaperture of varying size. Such mechanisms are frequently calibrated in"f-stops".

Once the optical image reaches the video pickup it is converted into anelectrical video signal. The pickup is used to generate a train ofelectrical pulses representing the light intensities present in theoptical image which is or has been focused on the surface of the pickup.Each point or pixel of this image is interrogated in its proper turn bythe pickup, and an electrical impulse corresponding to the amount oflight at that point is generated. Usually the electricaly impulses froma plurality of points are serially combined or concatenated to comprisethe video signal. In many pickup devices popular today, each point isinterrogated by an electron beam which is electrostatically ormagnetically deflected back and forth across a prescribed pattern(called a raster) on the glass target found on the inside of the pickupdevice. Electronic deflection circuitry generates electrical waveformswhich, when applied to deflection coils or the like, produce a linearscanning motion of the electron beam following the prescribed rasterpattern. To improve the image it is common to generate an interlacedraster, whereby all odd numbered lines are first sequentiallyinterrogated, followed by a vertical retrace of the beam to its point oforigin, and then all even numbered lines are sequentially interrogated.During vertical retrace the electron beam is swept, usually diagonally,from its termination point at the end of the last line in the rasterpattern or field to its origin point. During vertical retrace a blankingsignal is generated for a duration or blanking interval sufficient toallow the beam to sweep from termination point to origin point. Theblanking signal causes the pickup device to momentarily cut off itssignal output so that retrace lines are not visible when the image isviewed or replayed.

Most present day video pickups comprise electron tubes although thereare also solid state devices. Such electron tubes may be classifiedbased on the method of signal generation. In a non-storage tube, theonly light utilized in generating a signal is that light reaching aparticular point on the tube's light sensitive region while that pointis being scanned or interrogated. In a storage tube, on the other hand,an electric charge accumulates on the tube's light sensitive region ateach point during the interval between successive scans for laterinterrogation. Because the storage type tube uses the electric chargesgenerated by the light during the comparatively long intervals betweensuccessive scans of the image, it is more efficient and more sensitive.Storage-type tubes are further classified according to whether the lightsensitive element is photoemissive or photoconductive. Whenphotoemissive materials absorb light they emit electrons. Whenphotoconductive materials absorb light their electrical conductivitychanges.

The "vidicon" tube is one such photoconductive storage tube which hasgained great popularity due to its small size and simplicity ofoperation. The vidicon is a storage type tube in which the signal outputis developed directly from the target of the tube and is generated by alow velocity scanning beam from an electron gun. The target consists ofa transparent signal electrode deposited on the face plate of the tubeand a thin layer of photoconductive material, which is deposited overthe electrode. The photoconductive layer serves two purposes. It is thelight sensitive element, and it also forms the storage surface for theelectrical charge pattern that corresponds to the light image falling onthe signal electrode. The photoconductive material has a fairly highresistance when in the dark. Light falling on the material excitesadditional electrons into a conducting state, lowering the resistance ofthe photoconductive material at the point of illumination. In operation,a positive voltage is applied to one side of the photoconductive layervia the signal electrode. On the other side of the layer the scanningelectron beam deposits low velocity electrons in sufficient numbers tomaintain a net zero voltage. In the interval between successive scans ofa particular spot, the incident light lowers the resistance in relationto its intensity. With the resistance lowered, current flows through thesurface of the photoconductive layer and a positive charge is built upon the back surface of the layer; that positive charge is then helduntil the beam returns to scan the point. When the beam returns, asignal output current is generated at the signal electrode as thispositively charged area returns to zero voltage.

In order to provide low velocity electrons in a uniform manner, a finemesh screen is stretched across the interior of the tube near thetarget. The screen is energized to cause the electron scanning beam todecelerate uniformly at all points and to approach the target in aperpendicular manner. The beam is brought into sharp focus on the targetby longitudinal magnetic fields produced by focusing coils surroundingthe tube. The beam is made to scan the target in its characteristicraster pattern by varying magnetic fields produced by horizontal andvertical deflection coils also disposed about the tube.

Video systems of the prior art, including those using storage tubedevices, have been historically plagued with difficult and troublesomeblurring, skewing and distortion when used to produce slow motion orstop-action images. Slow motion and stop action images are createdduring playback by utilizing specially equipped video tape decks. Suchtape decks, however, can only produce images as clear and sharp as thevideo camera which produced them. If the video camera produces blurred,fuzzy or distorted images, then the taped image will also be blurred,fuzzy and distorted. These undesirable effects are most apparent duringslow motion or stop-action replay.

A prior art solution to the problem of blurred images is to interpose arotary shutter between the lense and pickup of an otherwise standardvideo camera. The rotary shutter of the prior art comprises a circulardisk provided with at least one matched pair of apertures spaced 180°apart about the circumference. The disk is rotated at a constant speedin use (typically 1800 rpm). The apertures are positioned about a locusbetween lenses and pickup so that for two brief intervals per diskrevolution, light images will illuminate the pickup tube. The aperturesare pie-shaped openings or segments bounded by radial lines emanatingfrom the center of rotation of the disk. Thus, by virtue of the factthat the pie-shaped apertures are paired and spaced 180° apart, 3,600individual or discrete exposures are made each minute at a rotationalrate of 1800 rpm. The exposures are timed to occur during the blankingintervals, hence each full raster interrogation produces a train ofelectrical impulses which represents the image exposed during a previousblanking interval. By using very short time intervals a fast movingobject, such as a rocket sled, or an athletic event, can be captured,stored and reproduced with less blurring or fuzziness than without theshutter. However, shutters of the prior art have been heretofore limitedto shutter speeds fo no faster than 1/10,000 second. While this mightseem quite fast, in high speed motion studies, during athletic events,and so forth, there are numerous events which cannot be capturedsatisfactorily at this shutter speed.

Moreover, there has heretofore been an unsolved problem associated withfast shutter speeds. Too fast a shutter speed can effectively reduce theoverall quantity of light reaching the pickup to the point where thepickup cannot properly respond. One solution is to open the lenseaperture, if one is provided, to a wider f-stop-which has its owndrawbacks, among them being a degredation in depth of field. Anothersolution is to provide other, slower shutter speeds. Thus, prior artshutters are frequently provided with a plurality of different sizedmatched pairs of pie-shaped apertures, each pair corresponding to adifferent discrete exposure time or shutter speed. With such anarrangement, however, it is not possible to continuously vary theshutter speed. One cannot, for example, select a shutter speed betweeentwo discrete speeds. Furthermore, in order to change shutter speedsusing prior art systems, it is necessary to first stop the rotatingshutter mechanism and lock it in place while indexing the mechanism to anew shutter speed. Varying the shutter speed while the shutter is inmotion (while recording a scene, for example) is not possible with priorart systems. Hence, such systems cannot be made to readily react totransient changes in light levels, such as might be caused by a passingcloud.

Another problem with prior art rotary shutter devices stems from the useof a pie-shaped shutter opening. Video pickup tubes usually have arectangular format, e.g. 4:3 width-to-height ratio. To evenly illuminatea rectangular pickup surface the shutter aperture must be constructed tosweep across equal areas at equal rates on both sides of the diagonal ofthe rectangular surface. In other words, the rectangular pickup must beoriented so that one of its vertical or horizontal centerlines coincideswith the radial lines which bound the pie-shaped shutter aperture.Although there are an infinite number of locations for the rectangularpickup about 360° arc, only four of these locations (located 90° apart)result in a horizontally or vertically disposed picture tube format thatcan be swept evenly by a pie-shaped opening. All other orientationsresult in a pickup surface which is skewed unnaturally to the opening.The undesirability of having a skewed format is evident when onerecognizes that the camera (or viewing screen) would always have to beheld or shimmed at an angel in order to render horizontal surfaceshorizontal and vertical surfaces vertical.

By constraining the location of the pickup tube relative to the shuttermechanism, the overall physical design of the camera (i.e., the size,shape, and bulkiness) is appreciably affected. Such restraints, as apractical matter, result in a larger, bulkier, less aestheticallypleasing and more cumbersome to operate camera than would otherwiseresult were the camera designer free to place components neatly andcompactly in aesthetically pleasing packages with all controlsconveniently located at the fingertips.

SUMMARY OF THE INVENTION

Accordingly, in order to improve upon prior art shutter mechanisms forvideo cameras, the present invention provides a shutter mechanism whichis capable of operating at vastly increased shutter speeds for sharper,clearer images and for less skewing and distortion. Fast moving objectsmay be studied in slow motion or stop-action with greater clarity.Shutter speeds may be varied over a continuous range, as opposed to indiscrete steps, and the shutter speed may be varied over this continuousrange while the shutter is operating. Hence, with the present invention,it is no longer necessary to stop the shutter while indexing to a newshutter speed. This enables the video camera to automatically respond tomomentary changes in lighting, resulting in a proper exposure at alltimes. In addition, the invention permits the video pickup device to beplaced anywhere in a 360° arc about the rotational axis of the shutter.Hence, design constraints inherent to prior art video cameras areeliminated.

In accordance with the invention, a focal plane shutter for a videocamera is provided comprising a disk mechanism positioned between thelense and pickup tube or device of the video camera for rotation aboutan axis. The video pickup device will be understood to include multipledevices, such as three tube or three device cameras, and other multiple(6, 12, 14, etc.) pickup systems. "Chip" cameras using a plurality (e.g.75,000-300,000) of individual sensors, as well as memory chip andcomputer enhanced cameras are also contemplated as within the scope ofthe invention. Rotation of the disk mechanism about the axis defines anannular locus which is in registration with the pickup and lense. Thedisk mechanism is provided with a single light-admitting apertureintersecting or lying within the locus, whereby the disk mechanism,except for the aperture, is opaque to the passage of light between thelense and the pickup. The invention also comprises a means for rotatingthe disk mechanism. The disk mechanism is disposed in a certain relationrelative to the pickup in order to block light from reaching the pickupat all times, except during a single, uninterrupted interval occurringnot more than once each revolution of the disk mechanism and lasting forless than the period of revolution.

The invention further comprises a focal plane shutter in which the diskmechanism is made up of a first disk disposed between the lense andpickup for rotation about an axis and a second disk disposed between thelense and pickup for rotation about the same axis. Rotation about theaxis defines an annular locus in registration with the pickup and lense.Both first and second disks are provided with an opening in registrationwith or intersecting the annular locus. These openings are registrableby properly adjusting the angular position of one disk in relation tothe other disk to define a light admitting aperture between the lenseand the pickup. A means is provided for rotating the first and seconddisks at a common speed. In addition, means are provided for adjustingthe relative angular positions of the disks relative to one another tothereby adjust the size of the light admitting aperture.

Further, the invention also provides a focal plane shutter for a videocamera having a disk disposed between lense and pickup for rotationabout an axis, the disk having a light admitting opening bounded onfirst and second sides by lines emanating from a point on the diskoffset from the axis of rotation. Preferably, the offset distance isdetermined in accordance with the diagonal dimension of the video pickupsurface.

These and other objects and advantages of the present invention willbecome more apparent from the following description and with referenceto the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a video camera which employs the shuttermechanism of the present invention;

FIG. 2 is an exploded diagrammatic view illustrating the shuttermechanism of the present invention in conjunction with a lense systemand video pickup;

FIG. 2a is a fragmentary view of the shutter mechanism of FIG. 2;

FIG. 3 is a schematic view of an exemplary video pickup tube in use withthe present invention;

FIG. 4 is a diagrammatic illustration of a raster scan pattern useful inunderstanding the operation of the invention;

FIG. 5 is a diagrammatic illustration of the rectangular raster area ona video pickup face plate, showing the swept illumination thereof as theshutter mechanism rotates;

FIG. 6 is a plan view of an alternate shutter disk configuration;

FIG. 7 is a plan view of a first shutter disk in accordance with theinvention;

FIG. 8 is a plan view of a second shutter disk in accordance with theinvention;

FIG. 9 is a perspective view of the disks of FIGS. 7 and 8, in relativeangular position to one another to create a large light admittingaperture;

FIG. 10 is a similar perspective view showing the disks of FIGS. 7 and 8in a different relative angular position to create a relatively narrowlight admitting aperture;

FIG. 11 is a rear elevation view showing a preferred shutter rotatingand adjusting mechanism in accordance with the invention;

FIG. 12 is a cross sectional view of the shutter mechanism shown in FIG.11, taken along line 12--12 of FIG. 11;

FIG. 13 is a cross sectional view of the shutter mechanism shown in FIG.11, taken along line 13--13 of FIG. 11;

FIG. 14 is an exploded perspective view of the primary components of theshutter mechanism of FIGS. 11-13;

FIG. 15 is a fragmentary view of the shutter mechanism illustratinganother embodiment;

FIGS. 16-18 illustrate another embodiment of the invention, particularlyan alternate mechanism for adjusting the shutter disks;

FIG. 19 illustrates another embodiment of the invention particularly ahydraulic system for adjusting the relative angular relationship of theshutter disks;

FIG. 20 is a cross sectional view of the shutter mechanism shown in FIG.19, taken along line 20--20 of FIG. 19;

FIG. 21 is a plan view of a different shutter disk configuration;

FIG. 22 is a diagrammatic view of a shutter disk showing the size, shapeand location of the light admitting opening in greater detail; and

FIGS. 23-26 illustrate still another alternate mechanism for adjustingthe shutter disks, with FIG. 24 being a cross-sectional view taken alonglines 24--24 of FIG. 23.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first to FIG. 1, a video camera in accordance with the presentinvention is illustrated at 20. The camera includes case or housing 22,AC/DC adapter 23, electronic viewfinder 24, viewfinder attachment boom25 and lense 26. The lense 26 is mounted to the front cover 30 of theshutter member 41. The lense 26 has a C-type mount and automatic focusand automatic zoom features operated by a servo motor mechanism 27.Power for operation of the servo mechanism is achieved through cord orwire 28 which is connected to the camera by plug 29. The electronicviewfinder 24, which is adapted to be mounted optionally on the back ofthe camera 20, is connected to the camera by cord or wire 31. The AC/DCadapter 23 converts the incoming AC power source to DC power for use inoperating the various mechanisms of the camera. A bracket or "shoe" 33is positioned on the top of the camera 20 for mounting of variousaccessories, if desired, such as an additional light source. Amicrophone 35 is provided to pick up the audio signals from the subjectbeing video taped. A mounting plate (not shown) or shoulder brace (alsonot shown) are also provided on the bottom of the camera 20 for use inmounting or using the camera.

The shutter member 41 has an adjust knob 43 (or "thumb wheel") whichprotrudes through the edge of the front cover 30 and is used by theoperator to adjust the shutter speed. The adjustment mechanism 32 whichis connected to the knob 43 and which actually adjusts the shutter speedis discussed in detail below. Also, as discussed below, the adjustmentmechanism 32 is all located rearward of the front cover 30 which leavesthe front cover flat and with ample room for manual or automatic zoomlense mechanisms. Since the lenses typically use C-type mounts whichscrew onto the camera, an adapter which would change the focal qualityof the camera would be required if the front cover 30 was not flat.

In the present preferred embodiment of the invention, the camera 20 hasa Sony chassis which has been modified to make it wider and longer. TheSony chassis has a 2/3" SMF Trinicon pickup tube.

FIG. 2 illustrates a few important components of the video camera 20,with exterior housing 22 and most internal components eliminated. Avideo pickup device 36, such as a video pickup tube, is disposed in linewith lense 26 as along the common axis 38 between lense 26 and videopickup 36. Video pickup 36 may be implemented using any of a widevariety of video pickup devices including vidicon tubes, saticon tubes,newvicon tubes, plumbicon tubes, chalnicon tubes, and the like. Also,solid state pickup devices, including optically sensitive random accessmemory devices (RAM), may be used. The invention is also equallyapplicable to systems using multiple pickup devices, such as a threepickup tube system for color video recording. Hence the term "videopickup device 36" will be understood to include such multiple pickupdevices.

Video pickup device 36 has a faceplate 40 onto which the optical imageis projected. The video pickup device 36 converts this optical imageinto a continuous stream of electrical impulses representing the image,and this stream of impulses may be magnetically encoded for storage on amagnetic video tape. While the images are being recorded, the stream ofvideo information may also be fed to electronic view finder 24 or to avideo monitor for an immediate review of the program material as it isbeing recorded.

Also shown in FIG. 2 is the disk shaped rotary focal plane shuttermechanism 42 which is one of the principal components of the shuttermember 41. In the preferred embodiment, shutter mechanism 42 comprises afirst disk member 44 which is positioned adjacent lense 26, and a seconddisk member 46 which is positioned adjacent pickup 36. Shutter mechanism42, including first disk 44 and second disk 46, is positioned betweenlense 26 and pickup 36 and supported for rotation about a central axis48. As shutter mechanism 42 rotates about axis 48 an annular locus 50 isdefined by and remains in registration with faceplate 40 of video pickup36. The same locus 50 is also in registration with the mounting end 52of lense 26. Generally speaking, locus 50 may be considered as theannular portion of shutter mechanism 42 which is illuminated by lightemanating from end 52 of lense 26 or which lies directly adjacentfaceplate 40.

Shutter mechanism 42 is provided with a light admitting aperture 54which lies generally within or intersects locus 50 to permit lightemanating from end 52 of lense 26 to reach faceplate 40 of video pickup36. Except for aperture 54, the remainder of shutter mechanism 42 isopaque to the passage of light.

In a presently preferred embodiment, the light admitting aperture 54 iscomprised of a pair of openings in registration with one another asshown in FIG. 2a. First disk 44 is provided with opening 56 and seconddisk 46 is provided with opening 58. Disks 44 and 46 may be rotatedabout central axis 48 until openings 56 and 58 intersect or overlap todefine the light admitting aperture 54. By altering the angularpositions of the disks 44 and 46 relative to one another, the size oflight admitting aperture 54 can be continuously varied from a thin slit(shown in FIG. 10), through intermediate sized apertures, to a fullsized aperture (shown in FIG. 9) which results when openings 56 and 58are in perfect coincident registration. Preferably openings 56 and 58are the same size and shape.

With reference to FIG. 3, video pickup 36 is shown schematically. Forpurposes of illustrating the invention, video pickup 36 is shown as avidicon tube, however, it will be appreciated that the invention isequally applicable to video camera systems using other types of videopickup devices, including solid state devices. Hence, the invention isnot intended to be limited to any particular type of video pickup. Thevideo pickup device illustrated in FIG. 3 is denoted generally byreference numeral 36, and includes a cylindrical glass tube 60 on whichglass faceplate 40 is secured or integrally formed. Pickup 36 has atarget section 62 comprising a transparent signal electrode 64 depositedon the inside of faceplate 40 and a thin layer of photoconductivematerial 66 which is deposited over electrode 64. The photoconductivematerial has a fairly high resistance when in the dark. Light falling onthe material excites additional electrons into a conducting state,lowering the resistance of the material at the point of illumination.Video pickup 36 also includes an electron gun 68 which may be energizedto produce an electron beam. Horizontal and vertical deflecting coils 70deflect the electron beam in accordance with horizontal and verticaldeflection circuitry 72 to produce a raster scanning pattern on thetarget section 62. A fine mesh screen 74 stretched across tube 60 neartarget section 62 causes the electron scanning beam to decelerateuniformly at all points and approach the target in a perpendicularmanner. The beam is brought to a sharp focus on target section 62 bymeans of longitudinal magnetic fields produced by a focusing coil 76which is energized at the proper focusing voltage by voltage source 78.The video signal output is coupled via output lead 80 to signalamplifying and processing circuitry 82. The signal output on output lead80 constitutes a video signal.

In operation, a positive voltage is applied to one side of thephotoconductive layer 66 by means of the signal electrode 64. On theother side of the photoconductive layer 66 the electron scanning beamdeposits low velocity electrons in accordance with a predeterminedraster scan pattern. A typical raster scan pattern is illustrated inFIG. 4 as it would be viewed from outside faceplate 40. As shown in FIG.4, the raster pattern 84 is generally rectangular, having horizontaldimension 86, vertical dimension 88 and a pair of diagonals 90 and 92which intersect at the raster center point 94. Raster pattern 84 isproduced by successive horizontal sweeps of the electron beam or lines.By convention, these lines are numbered consecutively beginning withline No. 1 at the bottom of raster pattern 84. Scanning starts at thebottom since the image is inverted by the lense. The number of lines mayvary depending upon the resolution of a particular video system. Atypical system might have 525 lines, for example. To minimizeflickering, the raster pattern is frequently generated by interlacingthe odd and even fields. This is accomplished by first scanning all oddnumbered lines (referred to as the odd field), and by then scanning alleven numbered lines (the even field). By convention, both the odd andeven fields commence in the lower right hand corner or origin point 96and end in the upper left hand corner or termination point 98. Eachfield is generated by sweeping back and forth; for example, Line 1 isswept from right to left, Line 3 from left to right, Line 5 from rightto left, etc. When the scanning beam reaches the termination point 98 itis swept diagonally generally along diagonal line 92, to the originpoint 96. This diagonal sweep is called the vertical retrace. During thetime in which vertical retrace occurs, the video signal is blanked bymeans of blanking circuitry 100 (FIG. 3) so that the diagonal retraceline is not visible.

As previously discussed, in the interval between successive scans of aparticular spot on target section 62, any incident light illuminatingthat spot lowers the resistance of the photoconductive layer at thatspot in relation to the light's intensity. Current then flows throughlayer 66 causing the back surface thereof to build up a positive chargeuntil the beam returns to scan the spot. A video output current pulse isgenerated at that spot on signal electrode 64 when the beam restores thepositively charged spot to a zero voltage. As the beam continues toscan, these current pulses are continually emitted to make up the videosignal.

With continued reference to FIG. 3, disks 44 and 46 are axially rotatedby motor 102 which is attached to the back cover plate 45 of shuttermember 41 and protrudes into the housing 22. In the presently preferredembodiment, motor 102 drives disks 44 and 46 at nominally 3600 rpm.Rotation is clockwise as viewed from the motor side, or counterclockwise as viewed from the lense side. Both the disks are oriented sothat openings 56 and 58 are in partial or full registration to definethe light admitting aperture 54 through which light from lense 26 isprojected onto faceplate 40. Motor 102 rotates disks 44 and 46 so thatan image will be projected on faceplate 40 once in each revolution. At arotation of 3600 rpm, 60 separate exposures per second are projected onfaceplate 40. These exposures are timed to occur during the blankinginterval when the scanning beam is executing a vertical retrace. Duringthe remainder of time, faceplate 40 receives no light through the opaquedisks. Hence, the scanning beam always interrogates an unchanging visualimage stored in the photoconductive layer 66 during a vertical retrace.Because the image is unchanging (no new light is admitted to change theimage), the resultant video signal on lead 80 represents a sharp,unblurred video image. Since 60 such individual exposures are made eachsecond, no perceptible flicker is evident when the video signals areviewed on a video monitor.

With reference to FIG. 5, it will be seen that the rotation of disks 44and 46, which cooperate to form shutter mechanism 42, causes faceplate40 to be swept with light once per revolution. As indicated above, it ispresently preferred to illuminate faceplate 40 during the verticalretrace interval of the raster scan cycle. The vertical retrace occursat repeated intervals determined by the electron beam scanning rate andthe number of lines which make up the raster. Thus, in many practicalapplications the illumination of faceplate 40 occurs at intervalscorresponding to the periods between vertical retrace cycles which areelectronically predetermined. By employing a single light admittingaperture 54 the present invention enjoys the highest possible shutterspeed or sweep rate for any given retrace period. To demonstrate this,FIG. 5 may be compared with FIG. 6 which illustrates an alternativeshutter member 104 having two light admitting apertures 106 and 108equally spaced about annular locus 50. Using the shutter mechanism ofFIG. 6, the speed of rotation must be half that of shutter mechanism 42in FIG. 5 in order to illuminate faceplate 40 at the same timeintervals. As indicated, these time intervals are often dictated by andoccur in synchronism with the vertical retrace cycle. Hence, the shutterspeed, or the speed at which light is swept across faceplate 40, of thetwo-aperture embodiment of FIG. 6 is one-half that of thesingle-aperture enbodiment of FIG. 5. A practical effect is that thesingle-aperture embodiment illuminates faceplate 40 for half as long asthe two aperture embodiment for each illumination interval. Thesingle-aperture embodiment is thus capable of capturing sharp images offast moving objects which appear as a blur through the two-apertureembodiment.

Preferably disks 44 and 46 are thin circular disks of aluminum ortitanium which are supported for rotation about their respectivegeometric centers. In order to place the inertial centers of the disksat their geometric centers, the disks are provided with counterbalancingcutout regions. These counterbalancing cutouts cause each disk's centerof mass to coincide with its geometric center. Hence, when the disks arespun, the polar moment of inertia is zero or substantially zero. FIG. 7illustrates disk 44 which is provided with cutout region 110; and FIG. 8illustrates disk 46 which is provided with cutout regions 112. Cutoutregion 110 on disk 44 is disposed at an average distance 148 from thegeometric center 114 that is different from the average distance 150 atwhich cutout regions 112 are disposed on disk 46. Thus, when disks 44and 46 are spun about central axis 48 through their common geometriccenters 114, cutouts 110 and 112 nowhere overlap. Thus, shuttermechanism 42, comprising disks 44 and 46 remain opaque to the passage oflight (except at the aperture 54), notwithstanding the fact that bothindividual disks 44 and 46 are provided with cutouts. FIGS. 9 and 10illustrate disks 44 and 46 in overlapping disposition exemplary of twopossible aperture sizes. In both Figures, note that cutouts 110 and 112nowhere overlap. Further in this regard, since both disks 44 and 46 arerotated as a common unit or in phase with one another, the cutouts 110and 112 do not in normal operation overlap with openings 56 and 58.

Unlike the situation with prior art focal plane shutters, the focalplane shutter of the present invention permits the operator tocontinuously vary the shutter speed while the shutter is in motion.Although the shutter mechanism 42 rotates at a constant speed insynchronism with the raster scan pattern, the relative size of aperture54 may be continuously varied by a number of different mechanisms toalter the shutter speed. In this regard, the shutter speed will beunderstood as a measure of the length of time during which the image isprojected on a given point on faceplate 40 during a given revolution ofshutter mechanism 42. In general, the larger the relative size ofaperture 54, the longer an image is projected on faceplate 40, and hencethe slower the shutter speed. Hence, FIG. 9 depicts the largest sizeaperture 54 corresponding to the slowest shutter speed; while FIG. 10depicts a relatively narrow or small aperture 54 corresponding to one ofthe fastest shutter speeds. In practice, utilizing disks 44 and 46having the size and shape shown in FIGS. 7 and 8, at a rotational speedof 3600 rpm, the invention will provide continuously variable shutterspeeds from nominally 1/500 to 1/20,000 second. The 1/20,000 secondspeed is achieved with an opening subtending a 1° arc.

A number of mechanisms may be alternatively used to change the relativeangular position of one disk with respect to the other and to therebychange the effective size of aperture 54. These mechanisms includemechanical linkages as well as hydraulic actuators. Alternatively, disks44 and 46 might also be rotated using separate phase-locked motorswherein at least one of the motors is driven by a source capable ofintroducing a phase lag or lead to thereby alter the relative angularposition of the disks to one another.

A preferred mechanism for mounting and operating the shutter mechanism42 is illustrated in FIGS. 11-14. The shutter member 41 comprises athin, relatively square shaped housing 47 which is adapted to be mountedby screws or bolts through openings 116 to the front of the case orhousing 22 of the video camera 20. The housing 47 is made of aluminum oranother material which has similar strength and weight characteristics,and which can be machined and formed in the shape and configurationsshown. The interior of the housing has one or more bores or recesses init, as described below, and the hollow interior is covered by back cover45. The back cover 45 is neatly positioned in recess 115 in the housingand held in place by a series of small screws 117.

The lense 26 is mounted on the front 30 of the housing 47. A stainlesssteel threaded lens ring 118 is pressfit in opening or bore 119 in thehousing and the end 52 of the lense 26 is threaded securely into it. Thevideo pickup 36 is positioned adjacent the back cover 45 of the hosuingon the same axis 38 as the lense. Typically, the video pickup isadjustable axiallly in the camera 20 for focusing. The distance Dbetween the faceplate 40 of the video pickup 36 and the end 52 of thelense 26 is between 0.400 and 0.500 inches and has to be maintained inthis range for proper focusing and operation of the camera withoutadditional adaptors and the like. If desired, the video pickup 36 can beattached to the housing 47 as shown in FIG. 12. A threadedannular-shaped ring 120 is secured, for example by screws 121, intorecess 122 in the back cover 45 and mates with threaded ring 123 on thevideo pickup 36. In this manner, the video pickup can be axiallyadjusted precisely and accurately.

A filter wheel 124 is interposed between the lense 26 and video pickup36. The wheel 124 has three filters 126 of various colors commonly usedin videotaping. The wheel 124 rotates on bushing 128 which is secured tothe housing 47 by screw 129. A portion of the wheel 124 protrudesoutside the housing 47 (as shown in FIG. 11) so that it can be manuallyrotated. For this purpose, the outside perimeter 125 of the wheel 124 isknurled or ribbed. When the wheel 124 is rotated, one of the filters 126becomes aligned axially with the lense 26, video pickup 36 and lightadmitting aperature 54 in the shutter disks 44 and 46. In this mannerthe light entering the video pickup from the lense is filtered asdesired. An indexing ball bearing 130 is set in a recess 131 in thehousing 47 and mates with one of four shallow recesses 132 in the filterwheel 124. The ball bearing and mating recesses act to index the filterwheel to one of four positions, three of which interpose a filter 126 inthe camera light path and the fourth of which prohibits any light fromentering the camera. The latter position of the filter wheel is used toprotect the expensive video pickup 36 during storage and handling of thecamera, or when the camera might be exposed to undesirable bright light.

As shown in FIG. 12, the filter wheel 124 is contained in a recess 134in the interior of the housing 47 and is also positioned between thedisks 44, 46 and the lense 26. It is also possible to arrange the partsso that the filter wheel is positioned between the disks 44, 46 and thevideo pickup 36. In either situation, the filter wheel will perform thesame function and be manually operated from outside the housing. Thefinal positioning of the filter wheel is determined by the dimension Dand by whether a mechanism is needed, such as ring 120, to hold and/oradjust the end of the video pickup 36.

A separate cover 136 is utilized to cover the filter wheel in thehousing 47. One edge 137 of the cover 136 is curved to match and matewith the edge of the circular back cover 45. Several screws 138 hold thecover 136 to the housing 47.

Disks 44 and 46 are provided with central openings 152 and 154,respectively, for mounting on a hub member 156. Hub member 156 isdisposed within or slightly below motor support housing 158 which inturn is secured to back cover 45 of housing 47. The support housing hasa flange 159 which is positioned in mating recess 160 in cover 45. Thehousing 158 is secured to the cover 45 by a number of screws 161. Motor102 is fastened to motor support housing 158 and is coupled to hubmember 156 for imparting rotary motion thereto. Disks 44 and 46 arefastened to hub 156 and rotate therewith. Central openings 152 and 154are each provided with a pair of tangentially extending slotted openings162-165. More specifically, central opening 152 is provided with a firstslotted opening 162 extending tangentially or spirally outwardly fromgeometric center 114, and a second slotted opening 163 extendingtangentially or spirally in a diametrically opposite direction toslotted opening 162. Similarly, central opening 154 is provided with afirst slotted opening 164 and a second diametrically opposing slottedopening 165. (For ease of reference, see FIGS. 7 and 8, as well as FIG.14.) When disks 44 and 46 are positioned in registration with oneanother on hub 156, the slotted openings 162-165 cross one another todefine a pair of V-shaped or X-shaped configurations as shown in FIGS. 9and 10. As explained more fully below, the precise configurationsdefined by the slotted openings determines the degree to which openings56 and 58 overlap, thereby defining the size of light admitting aperture54.

In order to change the configuration of the slotted openings 162 through165, pins 167 and 168 are slideably secured within hub 156 for radialmovement inwardly and outwardly with respect to hub axis 48. Hub 156 isprovided with a central opening 170. Hub member 156 is further providedwith an axial slot 175 for slideably receiving an arrowhead-shaped bladeaccuator 174 disposed on shaft 172. Shaft 172 is pressfitted orotherwise securely fastened at one end to drive shaft 173 of motor 102.Shaft 172 is fastened at its other end to the blade accuator 174 bybeing slip fitted inside cylindrical housing 176 which is secured to theblade. Shaft 172 has a slotted end 177 which slips over the blade. Theaccuator blade 174 is inserted into slot 175 and rests against the pins167 and 168.

Throw-out bearing mechanism 180 is securely fastened over shaft 172 andis coupled to a rocker arm or lever 181. Lever 181 is supported atfulcrum point 183 for rocking movement which causes the arrowhead-shapedblade accuator 174 to be translated along axis 48. Lever 181 has a yoke182 and is pivotably attached to bearing 180 by pins 185.

The inner ends of pins 167 and 168 bear against edges 184 and 186 ofblade 174 and radially translate inwardly and outwardly to follow edges184 and 186 as the accuator blade is moved axially in slot 175. Theouter ends of pins 167 and 168 bear against disks 44 and 46 at shoulders188 and 190. Specifically, shoulders 188 and 190 bear against portionsof disks 44 and 46 which define the perimeters of slotted openings162-164 (as best shown in FIGS. 9 and 10). Thus, radial movement of pins167 and 168 is translated into rotational movement of disks 44 and 46 inopposite directions to one another.

A pair of springs 192 and 194, disposed in arcuate-shaped slots 196 and198 in disks 44 and 46, bias disks 44 and 46 to rotate in directionsopposing the outward movement of the pins 167 and 168. (For ease ofreference the spring slots in disks 44 and 46 have both been marked withthe same reference numbers 196 and 198; curved slots 196 and 198 areidentical in both disks.) The relationship of the springs to the disksis best shown in FIGS. 9, 10, 12 and 14. One end of each spring 192, 194is hooked in a hole in one disk 44, 46 and the other end of each springis hooked in a hole in the other disk. For example, spring 192 has oneend 193 fastened in hole 193' in disk 44 and the other end 195 fastenedin hole 195' in disk 46. Similarly, spring 194 has one end 197 fastenedin hole 197' in disk 44 and the other end 199 fastened in hole 199' indisk 46.

When the springs 192 and 194 are at "rest" (in their untensionedposition), the openings 56 and 58 completely overlap (FIG. 9). At thisposition, the blade accuator 174 applies no force on pins 167 and 168.When the shutter speed is increased (i.e., the light admitting aperatureis made smaller) and the blade 174 pushed axially downwardly into hub156, the pins 167 and 168 are pushed outwardly into the "Vs" between thecentral openings of the disks. At this position (as illustrated in FIG.10), the springs 192 and 194 are extended and the force caused by thepins 167 and 168 overcomes the force of the springs. Later, when theshutter speed is decreased and the aperature 54 is enlarged, theaccuator blade 174 is retracted and the force of the springs 192, 194pushes the pins radially inwardly and tries to restore the discs totheir "rest" position.

The axial movement of the arrowhead-shaped blade 174 and thus theresultant opening and closing of the light admitting aperature 54 iseffectuated by movement of the lever 181. As indicated above, the lever181 is pivoted at fulcrum point 183 and one end is connected with a yoke182 to thrust bearing 180 and directly moves the blade accuator 174. Theother or distal end 202 of the lever 181 is fitted into a slotted cap204 containing a nylon mover 206 rotatably secured therein. The cap 204is secured to back cover 45 with screws 205.

The lever 181 protrudes through a slot 208 in the motor support housing158 and passes directly through a cap housing 210. The lever arm ispositioned in a rotatably mounted bushing 212 in the cap housing 210.The cap housing 210 is secured to the back cover 45 by screw 214.

Mover 206 has a beveled or angled surface 216 upon which distal end 202rides. Mover 206 is fastened to and a part of adjustment knob 43 whichwas previously described. The knob 43 rotates on a peg 218 in recess 219of housing 47 and has a knurled or ribbed edge 220 for manual rotation.Cover member 221 is positioned over the mover and adjustment knob andholds the knob in place on peg 218. The cover member 221 also acts asthe seat for slotted cap 204.

Adjustment of the shutter aperature 54 is controlled by the cameraoperator by manual rotation of the knob 43. As indicated earlier, theadjustment of the shutter aperature can be carried out while the disks44, 46 are rotating; the relative angular positions of the disks can beadjusted while they are rotating in a common direction about their axisof rotation. It is also possible for the shutter aperture to be adjustedautomatically, for example by means of a motorized system or linkagewhich is activated electronically by the outgoing video level.

As best shown by FIGS. 12-14, the disks 44 and 46 are positioned on thehub 156 and situated for rotation in a recess 135 in the interior ofhousing 47. The disks 44 and 46 are positioned next to each other onflange 222 and rest against larger flange 224. The disks are held on thehub by washer 226 and bearing 228. The bearing 228 is seated in bore 230in housing 47 and the hub is seated firmly in the bearing. Therelationship of the bearing 228, washer 226, disks 44 and 46, and flange224 holds the discs securely in position in the housing and on the hub,and yet allow them to rotate freely with the hub 156.

In operation, when the motor 102 is activated through appropriatecircuitry and controls 103 by the camera operator, the drive shaft 173with cylindrical shaft 172 attached thereto rotates the arrowhead-shapedblade accuator 174 which in turn rotates the hub 156 and the disks 44and 46. As indicated earlier, blade 174 is positioned in axial slot 175in hub 156.

Another arrangement for mounting the hub 156 for rotation in the shuttermember 41 is shown in FIG. 15. The hub 156 is situated for rotation inbearing 240 which in turn is seated in recess 242 in back cover 45.Bearing 240 at the upper end of the hub as shown in FIG. 15 replaces thebearing 228 at the forward end of the hub in the embodiment shown inFIGS. 12-14. Together with bearing 240, however, it is also possible touse, although it is not necessary, self centering pivot bearing 244. Ifutilized, bearing 244 is positioned in recess 246 in housing 47 andholds conical end 248 of hub 156.

To aid in the timing of the shutter system, sensor 250 and controlcircuitry 252 are provided. The sensor is positioned in opening 254 inback cover 45 and is set up to "read" painted dot 256 on disk 46. Thedot 256 is positioned at a prespecified and angular location fromopening 58 on disk 46 (and hence from light admitting aperature 54). Inthe embodiment shown, the sensor 250 is positioned 180° from theopening. The sensor senses the dot each revolution of the disc and,through the control circuitry 252, insures that the video camera systemis in the correct mode of operation when the disk openings 56 and 58 arein axial alignment with the video pickup 36. This arrangementcompensates for any fluctuations in the speed of the motor 102, anyphase-lock losses which might be encountered during adjustment of theshutter aperture, or any other changes or variations in the system whichmight affect the proper timing and orientation of the aperature 54 withrespect to the positions of the lense and video pickup.

An alternate mechanism for adjusting the shutter aperature and therelative angular rotation of the rotating disk relative to one anotheris shown in FIGS. 16, 17 and 18. This embodiment differs from thatdescribed above relative to FIGS. 11-14 in the arrowhead-shaped accuatorblade, the structure used to transmit the movement of the blade to therelative angular positions of the disks, the center openings of thedisks, and changes in the hub to incorporate these differences.

The disks 300 and 302 are shown in their operating stacked relationshipin FIG. 16. Each of the disks has a similar sized opening 304, 306 whichtogether act as the light admitting aperature 308 in the same mannerthat openings 56, 58 in disks 44 and 46 form aperature 54 discussedearlier. The disks 300, 302 also have balance openings 310 and 312 whichare similar in size, shape and function to the openings 110 and 112 indisks 44 and 46. The center openings 314 and 316 of the disks 300, 302are circular and are adapted to fit on and be turned by hub 318.

The accuator blade 320 is not as thin as blade 174 discussed above andadjusts the relative angular relationship of the disks in a differentmanner, but the general purpose of the blade 320 is the same. The blade320 is attached to a motor driveshaft 322 for rotation, fits inside androtates the hub 318, and is adapted to move axially along axis 48 toadjust the size of the aperature 308. Brackets 330 and 332 are slidinglysecured in channels 334, 335, 336 and 337 in blade 320 and protrude andmove radially outwardly from the hub 318 in passageways 340 and 341.Pegs 343 and 344 extend from brackets 330 and 332 and fit into slantedopenings 346, 347, 348 and 349 in the disks 300 and 302. Openings 346and 349 are in disk 300 and openings 347 and 348 are in disk 302. Theseopenings are arranged in pairs which overlap at a certain point and pegs343 and 344 extend through them.

As the accuator blade 320 is moved axially along axis 48, the bracketsand pegs move radially and slide within the slanted openings. As thepegs are forced radially outwardly, the slanted openings tend to crosswhich causes the disks 300, 302 to rotate relative to one another andthereby close the aperature 308. The process is repeated in the oppositedirection for the aperature to be widened. The embodiment of FIGS. 16-18does not utilize springs in the operation of the adjustment mechanismfor the aperture and less possible loading of the motor 102 shouldresult.

Other mechanisms for moving the accuator blade 174 axially in the slot175 can also be utilized. For example, in place of theknob-mover-lever-yoke mechanism shown and described relative to FIGS.11-14, it is also possible to provide a slotted ring attached to a slidemechanism for axial movement of the accuator blade. Such an alternatemechanism is shown in FIGS. 23-26.

The ring 281 has three elongated slots 283 positioned equidistantlyaround its circumference. The slots are angled approximately 30° fromthe horizontal (as illustrated by angle 285 in FIG. 25). The thrustbearing 287 is similar to thrust bearing 180 described earlier, but hasthree pegs 289 extending outwardly from it. The pegs 289 are positionedequidistantly around the circumference of the bearing and are slidinglypositioned in the slots 283. The thrust bearing is secured to shaft 172inside motor support housing 158. Lever 291 is attached to the outsideof the ring 281 and extends through a slot 293 in housing 158. The leveris connected to a slide mechanism (not shown) on the exterior of theshutter mechanism housing 47, preferably along an edge thereof. Movementof the slide mechanism causes a corresponding rotation of the ring 281around central axis 48. Rotation of the ring 281 due to the angled slots283 in turn causes a direct axial movement of the accuator blade 174along axis 48.

Still another embodiment for continuously adjusting the shutteraperature is illustrated in FIGS. 19 and 20. In this embodiment, ahydraulic mechanism is utilized which consists essentially of a mastercylinder and double piston arrangement. The master cylinder comprises asmall piston 360 slidably positioned in cylindrical bore 362 in housing363. The piston 360 has a seal 364 thereon which sealingly engages thewalls of the cylinder 362. A piston rod 336 is pivotably attached at oneend 368 to the piston 360 and is pivotably attached at the other end 370by screw 371 to an adjustment knob 372. The knob 372 has a knurled orribbed edge 374 for manual rotation and is rotably situated on pivot peg376.

A pair of pistons 380 and 382 are slidingly positioned in cylindricalbore 384 in hub 386. The pistons have seals 392 and 394 on their innerends for sealingly engaging the walls of the cylinder 384. A screw 396prevents the pistons 380 and 382 from touching or sliding past thecenter point in the cylinder, and also provides a port for "bleeding"the hydraulic system. The pistons have rounded ends 398 and 400 whichmate with the "X" or "V"-shaped configurations of the disks 388 and 390.The "X" or "V"-shaped configurations are not shown in FIGS. 19 and 20,but they are the same as the ones described earlier relative to FIGS. 9and 10. In this regard, the ends 398 and 400 of the pistons perform thesame function and operate in a similar manner as the radially extendedpins 167 and 168.

The hydraulic path between cylinders 362 and 384 includes passageway 402and recess 404 in housing 363, and passageway 406 in hub 386. All of theportions of the hydraulic path are filled with an apprioruate hydraulicfluid. A seal 408 seals the joint between the hub 386 and the walls 405of the recess 404. The seal 408 preferably is a spring seal with a smallspring 409 embedded in it and utilized to insure sufficient sealingqualities to the seal. The end 410 of hub 386 is rotationally positionedin the seal 408 and the hub is rotated by a motor (not shown). The driveshaft of the motor is mechanically connected to slot 412 on the top ofhub 386 and rotates it directly. The remaining features of the shuttermechanism shown in FIGS. 19 and 20 are the same as or the equivalent tothose described earlier.

In operation, the shutter aperature is adjusted by manual rotation ofthe knob 372. Rotation of the knob 372 slides the piston 360 axially inits cylinder and causes the hydraulic fluid in the system to actuate thepistons 380 and 382 in the hub. Activation of the pistons 380 and 382radially outwardly causes the ends 398 and 400 to be pushed or forcedinto the "X" or "V"-shaped configurations on the disks and therebyrotate the disks in opposite directions and close the light admittingaperature. When the aperature is desired to be made larger (and thus theshutter speed is desired to be slowed down), the knob 372 is rotated inthe opposite direction. This slides the piston 360 toward the knob andin turn "pulls" the pistons 380 and 382 toward each other in cylinder384 in the hub. Springs on the disks, such springs being similar tothose described above relative to FIGS. 9 and 10, act to rotate thedisks back toward their open-aperture position.

While a presently preferred embodiment employs a single light admittinglight aperture 54 for maximum hutter speed at a given exposure rate, thevarious mechanisms described above for continuously adjusting theshutter speed while the shutter is in motion are not limited to thesingle aperture embodiment. In general, the shutter speed adjustmentmechanisms of the present invention are equally useful with multipleaperture shutters, such as the two-aperture shutter of FIG. 6.Furthermore, while the presently preferred aperture is of a particularshape and location, yet to be discussed, the shutter speed adjustmentmechanisms are equally useable with other aperture shapes and locationssuch as the pie-shaped apertures 450 and 452 on disk mechanism 454, asillustrated in FIG. 21. As is apparent from FIG. 21, the side surfaces460, 462, 464 and 466 of the two openings 450 and 452 fall along radiansfrom the center 468 of the disk mechanism 454. Furthermore, theinventive concept of utilizing a single-aperture for maximized shutterspeed may be expoloited with shutters having shapes and locationsdiffering from the presently preferred shape and location shown in FIGS.7, 8 and 22 and more fully explained below.

With reference to FIG. 22, the presently preferred apertureconfiguration will now be discussed. In order to provide uniformillumination across faceplate 40, the aperture defining openings 56 and58 of disks 44 and 46, respectively, are formed with the unique shapeshown in FIG. 22 at the location shown. (The same shaped openings arealso shown in FIGS. 5-10.) Preferably openings 56 and 58 are identical,hence only opening 56 will be discussed herein. Opening 56 is bounded ona first side 470 by line 472 and bounded on a second side 474 by line476. Lines 472 and 476 both emanate from a point 478 on the surface ofdisk 44. Point 478 is offset at a predetermined distance 480 from thegeometric center 114 of the disk. (It will be recalled that the centralaxis of rotation 48 of the disks is through the geometric center 114.)Opening 56 is further bounded on third and fourth sides 482 and 484 bythe concentric inner and outer boundaries of annular locus 50. Lines 472and 476 define an acute angle 486.

In the presently preferred embodiment, the general size of opening 56 islargely determined by the size of faceplate 40, and more particularlydetermined by the size of the rectangular area 488 swept by the electronbeam during the raster scan. For convenience, rectangular area 488 willbe further described using the reference numerals used to describe theraster 84 of FIG. 4, where applicable. Point 478 is positioned at thepredetermined distance 480 from geometric center 114 such that a line400 bisecting angle 486 will coincide with one of the diagonals ofrectangular area 488. In FIG. 22, the bisecting line 490 overliesdiagonal line 92. Angle 486 is constructed so that lines 472 and 476 areroughly tangent to the circumference of pickup 40 when disk 44 isrotated to the position where bisecting line 490 and diagonal line 92coincide.

The predetermined distance 480 is preferably equal in length to eitherof the diagonal lines 90 or 92 of the raster 84. The precise location ofpoint 478 may be constructed by scribing an imaginary rectangle 494 onthe surface of disk 44, the imaginary rectangle being the exact size andshape of rectangular area 488. The imaginary rectangle 494 touchesgeometric center 114 at corner 496 and is rotationally oriented 90degrees with respect to rectangular are a 488. Point 478 is located atthe corner of imaginary rectangle 494 diagonally opposite corner 496.

By constructing openings 56 and 58 in accordance with the above, a moreeven exposure is obtained. The resulting aperture configuration allowsmore light to reach faceplate 40 for a given shutter speed or exposureduration. This results in a more sensitive overall video system andallows the aperture to be comparatively smaller for a given lightingsituation than with prior art shutters. The smaller aperture means afaster shutter speed, hence greater clarity and less blurring of fastmoving objects.

Furthermore, since rotation of the disks in counterclockwise (as viewedfrom the lense side), the unique shape of openings 56 and 58 cause thelower left corner 498 of rectangular area 488 to be swept first withillumination. since this lower left corner is also first to beinterrogated by the electron beam in the raster scanning pattern, theopical image is captured in the same sequence as it illuminates thepickup device. Hence any image decay occurs evenly across the entirepickup device.

While the invention has been described in its presently preferredembodiments, various changes in the details, materials, and arrangementof parts may be made by those skilled in the art within the principlesand scope of the invetnion and defined in the appended claims.

What is claimed is:
 1. A focal plane shutter for a video camera having alense and pickup comprising:disk means disposed between said lense andsaid pickup for rotation about an axis; said disk means having anopening bounded on first and second sides by lines emanating from apoint on said disk offset from said axis of rotation.
 2. A shutter for avideo camera having a pickup surface of a given diagonal dimension, inaccordance with claim 1, wherein said point is offset from said axis adistance substantially equal to said diagonal dimension.
 3. The shutterof claim 1 wherein said opening is further bounded on a third side by afirst arc having radius originating at said axis.
 4. The shutter ofclaim 3 wherein said opening is further bounded on a fourth side by asecond arc having radius originating at said axis.
 5. A shutter for avideo camera having a pickup surface on which a raster is defined, inaccordance with claim 1, wherein said point is located at a corner of animaginary plane figure of substantially the same size and shape as saidraster.
 6. The shutter of claim 5 wherein said imaginary plane figure isorthogonally oriented with respect to said raster.
 7. A shutter for avideo camera having a pickup surface of a given peripheral size, inaccordance with claim 1, wherein said opening is of a predetermined sizedetermined in accordance with said peripheral size of said pickupsurface.
 8. The shutter of claim 1 wherein said pickup has a peripheryand said lines bounding said first and second sides are approximatelytangent to said periphery.